96 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Hence "we see that the weather side of all such mountains as the 

 Andes is the wet side, and the lee side the dry. 



200. The same phenomenon, from a like cause, is repeated in 

 inter-tropical India, only in that country each side of the mountain 

 is made alternately the wet and the dry side by a change in the 

 prevailing direction of the wind. Plate VIII. shows India to be 

 in one of the monsoon regions : it is the most famous of them all. 

 From October to April the northeast trades prevail. They evap- 

 orate irom the Bay of Bengal water enough to feed with rains, 

 during this season, the western shores of this bay and the Ghauts 

 range of mountains. This range holds the relation to these winds 

 that the Andes of Peru (§ 194) hold to the southeast trades ; it 

 first cools and then relieves them of then' moisture, and they tum- 

 ble down on the western slopes of the Ghauts, Peruvian-like 

 (§ 199), cool, rainless, and dry ; wherefore that narrow strip of 

 country between the Ghauts and the Arabian Sea would, lil^e 

 that in Peru between the Andes and the Pacific, remain without 

 rain forever, were it not for other agents which are at work about 

 India and not about Peru. The work of the agents to which I 

 allude is felt in the monsoons, and these prevail in India and not 

 in Peru. 



201. After the northeast trades have blown out their season, 

 which in India ends in April (§ 200), the great arid plains of Cen- 

 tral Asia, of Tartary, Thibet, and Mongolia, become heated up ; 

 they rarefy the air of the northeast trades, and cause it to ascend. 

 This rarefaction and ascent, by their demand for an indraught, are 

 felt by the air which the southeast trade-winds bring to the equa- 

 torial Doldrums of the Indian Ocean : it rushes over into the 

 northern hemisphere to supply the upward draught fi:om the heat- 

 ed plains as the southwest monsoons. The forces of diurnal ro- 

 tation assist (§ 44) to give these winds their westing. Thus the 



~ southeast trades, in certain parts of the Indian Ocean, are con- 

 verted, during the summer and early autumn, into southwest 

 monsoons. These then come from the Indian Ocean and Sea of 

 Arabia loaded with moisture, and, striking with it perpendicularly 

 upon the Ghauts, precipitate upon that narrow strip of land be- 

 tween this range and the Arabian Sea an amount of water that is 



